1. Field of the Invention
The present invention relates to multicolor optical filters and a process for producing the same, particularly, to multicolor optical filters for color camera tubes and a process for producing the same.
2. Development of the Invention
In single-tube or two-tube type color camera tubes, multicolor striped or multicolor mosaic optical filters have been used. While generally the multicolor optical filters comprise three colors: red, green and blue or cyan, magenta and yellow, which are regularly arranged to form a striped or mosaic pattern, the color system is not limited to these three colors and optical filters of two colors or four or more colors can also be utilized.
Hitherto known multicolor optical filters include, for example, those using a dichroic membrane as described in Japanese Patent Publication No. 8590/65 and Japanese patent application (OPI) No. 3440/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), etc., and those wherein a high molecular weight material layer is colored with dyes as described in Japanese patent applications (OPI) Nos. 37237/72, 63739/73 and 66853/73 and Japanese Patent Publication No. 248/78, etc. However, processes for producing such filters are very complicated as they require the application of a photoresist for each respective color and pattern formation steps comprising imagewise exposure with correct mask arrangement, development, coloring or bleaching and removal of resists, which must be repeatedly carried out (generally, 3 or more times).
Further, in practice, various additional steps are required to obtain excellent multicolor optical filters, for example, in the case that a multicolor optical filter is produced by repeating the steps of application of a photoresist (such as bichromic acid-gelatin, etc.), imagewise exposure and relief pattern formation by development and coloring, it is necessary to insure that the color pattern formed in one stage does not discolor the color pattern of the next stage. For such purpose, it is necessary to apply a "noncoloring" protective layer to the surface of the pattern after each coloring stage, as described in Japanese patent application (OPI) No. 37237/72. Consequently, the production process becomes complicated and the resultant multicolor optical filter expensive.
Further, in multicolor optical filters for camera tubes, it is necessary to form a pure black pattern (so-called "optical black") in order to inspect the absolute zero value of input signals thereto, and chromium membrane patterns formed by a lithographic process have been used for optical black (referred to as "O.B." hereinafter) having a high optical density since such O.B. can be easily obtained if an evaporated or sputtered chromium layer is used.
In the following, an example of a typical process for producing a multicolor optical filter according to the prior art is illustrated with reference to drawings.
FIG. 1 illustrates a process for producing a multicolor optical filter having O.B. according to the prior art, where FIG. 1a to FIG. 1e illustrate forming O.B. on a base and FIG. 1f to FIG. 1h illustrate forming one color of the multicolor optical filter on the base on which O.B. was formed.
FIG. 1a shows a glass base 10 on which a thin chromium layer 11 is provided by vacuum evaporation or sputtering to have a high optical density; in FIG. 1b photoresist layer 12 has been applied to the thin chromium layer 11; in FIG. 1c photoresist layer 12 has been developed to form opening 14 and etching resist 13 after the photoresist layer 12 was exposed to light of the desired O.B. pattern; in FIG. 1d the chromium layer 11 has been removed under opening 14 by, for example, chemical etching to expose area of the glass base thereunder 15; in FIG. 1e O.B. 16 is formed by removing the photoresist.
After O.B. 16 was formed on the glass base 10 in the above manner, a multicolor optical filter is formed as now illustrated with reference to the case of dyeing bichromic acid-gelatin; in FIG. 1f a light sensitive hydrophilic polymer layer 17 (such as a bichromic acid-gelatin layer) is provided on the whole surface of the element; in FIG. 1g a striped relief pattern 18 of the hydrophilic polymer is formed by development after layer 17 is subjected to striped pattern exposure; in FIG. 1h stripe filter 19 is formed by dyeing the resultant relief with a dye.
Thus, a first color stripe filter having O.B. is obtained. After the first color stripe filter is formed, a water-impermeable protective layer is applied to prevent color mixing and the steps of FIG. 1f to FIG. 1h repeated to form a multicolor optical filter.
Such a process for producing a multicolor optical filter for camera tubes has the drawback that the multicolor optical filter is expensive because a lithographic process is required to form O.B. of a thin chromium layer in addition to the above described complicated color pattern forming steps.
The present inventors have developed a process which comprised using a known prior photographic material having a black-and-white silver halide emulsion layer in combination with a color development process using a coupler-containing developer, whereby multicolor optical filters are easily produced at low cost as compared with the prior art multicolor optical filters, which process was proposed in co-pending application Ser. No. 52,704, filed June 28, 1979.